1. Field of the Invention
The present invention relates to a camera having incorporated therein an optical filter for a photographic lens.
2. Description of Related Art
In a TTL single-lens reflex camera, which is arranged to guide light having passed through the photographic lens to a viewfinder, when the photographer intends to use a polarizing filter or the like, he or she screws and fixes a male screw of a mounting part of the polarizing filter or the like to a female screw provided on a fore end of a photographic lens barrel. With the polarizing filter or the like fixed to the photographic lens barrel, the photographer manually rotates the polarizing filter or the like around an axis parallel with the optical axis of the photographic lens while looking into the viewfinder of the camera (as some of the polarizing filters or the like are arranged to be rotatable with the mounting part thereof), and adjusts the rotated position of the polarizing filter or the like while confirming with his or her eye a viewfinder image to obtain a desired filter effect, before taking a photograph.
To solve the above inconveniences of mounting and demounting the filter, there has been proposed, in Japanese Laid-Open Patent Application No. Hei 8-334809, a camera in which a filter incorporated therein is arranged to be electrically driven to advance to the inside or retreat to the outside of an optical path of a photographic lens.
In addition, in Japanese Laid-Open Patent Application No. Hei 5-34116, there has been proposed such a technical art that two poralizing filters are disposed in a lens barrel of an interchangeable lens for the video camera or the like and one of the two poralizing filters is arranged to be rotated by an actuator so as to serially adjust the amount of light for the interchangeable lens (in particular, a mirror lens).
Further, since, in a lens-shutter camera, the optical axis of a photographic lens is provided separately from that of a viewfinder, the photographer cannot view image light having passed through the photographic lens and, therefore, cannot recognize, through the viewfinder, the effect of a polarizing filter or the like mounted on the fore end of a photographic lens barrel. Accordingly, the photographer need adjust the rotated position of the polarizing filter or the like by means of an index provided on a mounting frame of the polarizing filter or the like with the eye measurement, before taking a photograph.
In Japanese Laid-Open Utility Model Application No. Hei 3-60323, there has been proposed, in view of the above problem, a lens-shutter camera in which two polarizing filters that are rotatable in synchronism with each other are respectively provided on front surfaces of a photographic lens and a viewfinder. In such a camera, when the polarizing filter on the side of the photographic lens is rotated manually by the photographer, the polarizing filter on the side of the viewfinder is also synchronously rotated in the same direction, so that the photographer can recognize with the eye through the viewfinder the effect of the polarizing filter to be obtained during the taking of a photograph.
However, in the conventional TTL single-lens reflex camera, there is such an inconvenience that the photographer troublesomely must manually rotate the polarizing filter or the like to a desired position while always recognizing with the eye through the viewfinder the effect of the polarizing filter or the like. In addition, even if the photographer expects to have adjusted the rotated position of the polarizing filter or the like to such a position as to obtain the greatest filter effect, a little deviation would be necessarily caused, so that it is impossible to make the best use of the filter effect.
Further, in the case of a photo-taking operation requiring no polarizing filter or the like (for example, in the case of an object having low luminance, in a case where the effect of the polarizing filter or the like is little due to the backlighting situation or the like, or in a case where the amount of light emission resulting from a normal flash emission photo-taking operation is lost due to the presence of the polarizing filter or the like), the photographer troublesomely must remove the polarizing filter or the like with the hand upon his or her intention. Conversely, in the case of a photo-taking operation requiring the polarizing filter or the like suddenly, the photographer must perform such a very troublesome operation as to take out the polarizing filter or the like stored in a filter case and mount the polarizing filter or the like on the photographic lens barrel with the hand. Therefore, there are the great inconveniences of degrading the speedy photography and missing the shutter opportunity.
Further, in the cameras proposed in the above Japanese Laid-Open Patent Applications No. Hei 8-334809 and No. Hei 5-34116, even if it is possible to mount and demount the polarizing filter or the like incorporated in the camera by electrically driving the polarizing filter or the like to advance and retreat, the photographer troublesomely must operate a manual operation switch upon judging whether the polarizing filter or the like is required. In addition, if an electrical-driving advance/retreat mechanism for the polarizing filter or the like is provided in a lens barrel, a retreat space for making the filter entirely escape from the optical path as well as a space for the electrical-driving advance/retreat mechanism becomes necessary in a direction perpendicular to the optical axis. Therefore, a part of the lens barrel of the cylindrical shape would become greatly protrusive, so that there is the inconvenience of impairing an external design of the camera.
Further, if the mechanism for the filter is provided in the interchangeable lens, as proposed in the above Japanese Laid-Open Patent Application No. Hei 5-34116, the various filter mechanisms having the respective sizes which are individually adapted for the various interchangeable lenses of the TTL single-lens reflex camera system become necessary for obtaining the same filter effect. Therefore, there is the inconvenience of increasing the cost of the camera system.
Further, in most of the lens-shutter cameras, an external light measurement is employed in place of the TTL light measurement. Therefore, when the polarizing filter or the like is used, an exposure to be actually made on the film is obtained by light which is attenuated by passing through the polarizing filter, but a light measurement value of the camera remains unchanged. Accordingly, there is the inconvenience of making a taken photograph underexposed but for an exposure compensation.
Further, in most of the lens-shutter cameras, an external distance measurement is employed in place of the TTL distance measurement. Therefore, if the filter is inserted into the optical path of the photographic lens except for the front side of the photographic lens, a change in the optical path length would occur, so that the image forming position becomes different from that obtained when the filter is not inserted. Accordingly, there is the inconvenience of making the photographic lens out of focus if an automatic focus adjusting operation is performed without modifying distance measurement data obtained by the external light measurement.
Further, regardless of the TTL single-lens reflex camera or the lens-shutter camera, in a case where a close-up photography is performed mainly onto a plane-surface object (in particular, an object having a smooth surface) with flash light emission, the light emitted from a flash emitting device such as a stroboscope is reflected from the object and, then, is made to enter the inside of the photographic lens, so that highlight glare occurs. Accordingly, there is the inconvenience of making it impossible to take a sharp photograph.